Blowing Agent Enhancers for Polyurethane Foam Production

ABSTRACT

Rigid polyurethane blowing agent enhancers, methods for using them, and the products produced by these methods are disclosed. The enhancers are low molecular weight alcohols and/or ethers that assist the action of blowing agents comprising a hydrohalocarbon compound.

BACKGROUND OF THE INVENTION

The present invention relates to compositions and processes for makingpolyurethane foams. More particularly, it relates to compositions andprocesses incorporating compounds for enhancing the effectiveness ofhydrohalocarbon blowing agents in making polyurethane foams.

The manufacture of rigid polyurethane foams has been significantlyimpacted by restrictions on the use of certain prior art blowing agents,which may be environmentally harmful. Although new, more environmentallyacceptable blowing agents have come into use (typicallyhydrohalocarbons), these are generally not as effective as thosecommonly used previously and there is therefore a continuing need forenhancements in the process of making rigid polyurethane foams and/or inthe properties of the foams themselves. The present invention addressesthat need with compounds which are believed to enhance the effectivenessof blowing agents used in making rigid polyurethane foams.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention is a composition for producing apolyurethane foam. The composition comprises a polyol, a polyisocyanate,a blowing agent comprising a hydrohalocarbon, and a blowing agentenhancer comprising at least one compound having a molecular weight lessthan about 500 g/mol and a molecular formula of RO—(CH₂CHR″O)_(n)—R′;wherein:

R is selected from the group consisting of a C1-C10 aliphatic group, aC5-C10 cycloaliphatic group, a C7-C10 araliphatic group, a C1-C10aliphatic group comprising a nitrogen atom or oxygen atom, a C5-C10cycloaliphatic group comprising a nitrogen atom or oxygen atom, and aC7-C10 araliphatic group comprising a nitrogen atom or oxygen atom;

R′ is selected from the group consisting of R, hydrogen, acetyl,propionyl, and butyryl, provided that the at least one compound has nomore than one hydroxyl group per molecule;

R″ is hydrogen or a C1-C5 alkyl group; and ″

n is an integer greater than or equal to 1.

In another aspect, the invention is a method of making a polyurethanefoam. The method comprises combining a polyol and a polyisocyanate inthe presence of 1) a blowing agent comprising a hydrohalocarbon and 2) ablowing agent enhancer comprising at least one compound having amolecular weight less than about 500 g/mol and a molecular formula ofRO—(CH₂CHR″O)_(n)—R′; wherein:

-   -   R is selected from the group consisting of a C1-C10 aliphatic        group, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic        group, a C1-C10 aliphatic group comprising a nitrogen atom or        oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogen        atom or oxygen atom, and a C7-C10 araliphatic group comprising a        nitrogen atom or oxygen atom;    -   R′ is selected from the group consisting of R, hydrogen, acetyl,        propionyl, and butyryl, provided that the at least one compound        has no more than one hydroxyl group per molecule;    -   R″ is hydrogen or a C1-C5 alkyl group; and    -   n is an integer greater than or equal to 1.

In yet another aspect, the invention is a composition for producing apolyurethane foam. The composition comprises a polyol, a polyisocyanate,a blowing agent comprising a hydrohalocarbon, and a blowing agentenhancer comprising at least one compound having a molecular weight lessthan about 500 g/mol and a molecular formula ROH, wherein:

-   -   R is selected from the group consisting of a C1-C10 aliphatic        group, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic        group, a C1-C10 aliphatic group comprising a nitrogen atom or        oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogen        atom or oxygen atom, and a C7-C10 araliphatic group comprising a        nitrogen atom or oxygen atom, provided that the at least one        compound comprises only one hydroxyl group per molecule.

In a further aspect, the invention is a polyurethane compositioncomprising a product of a reaction between a polyol and apolyisocyanate. The reaction takes place in the presence of 1) a blowingagent comprising a hydrohalocarbon and 2) a blowing agent enhancercomprising at least one compound having a molecular weight less thanabout 500 g/mol and a molecular formula of RO—(CH₂CHR″O)_(n)—R′;wherein:

-   -   R is selected from the group consisting of a C1-C10 aliphatic        group, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic        group, a C1-C10 aliphatic group comprising a nitrogen atom or        oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogen        atom or oxygen atom, and a C7-C10 araliphatic group comprising a        nitrogen atom or oxygen atom;    -   R′ is selected from the group consisting of R, hydrogen, acetyl,        propionyl, and butyryl, provided that the at least one compound        has no more than one hydroxyl group per molecule;    -   R″ is hydrogen or a C1-C5 alkyl group; and    -   n is an integer greater than or equal to 1.

In a still further aspect, the invention is a composition for producinga polyurethane foam. The composition comprises 1) one but not both of apolyol and a polyisocyanate, 2) a blowing agent comprising ahydrohalocarbon and 3) a blowing agent enhancer comprising at least onecompound having a molecular weight less than about 500 g/mol and amolecular formula of RO—(CH₂CHR″O)_(n)—R′; wherein:

-   -   R is selected from the group consisting of a C1-C10 aliphatic        group, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic        group, a C1-C10 aliphatic group comprising a nitrogen atom or        oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogen        atom or oxygen atom, and a C7-C10 araliphatic group comprising a        nitrogen atom or oxygen atom;    -   R′ is selected from the group consisting of R, hydrogen, acetyl,        propionyl, and butyryl, provided that the at least one compound        has no more than one hydroxyl group per molecule;    -   R″ is hydrogen or a C1-C5 alkyl group; and    -   n is an integer greater than or equal to 1.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves the use of low molecular weight ethersand alcohols as blowing agent enhancers for improving the efficiency ofhydrohalocarbon blowing agents in the preparation of rigid polyurethaneand/or polyisocyanurate foam. As used herein, the term “polyurethane” isintended to mean polyurethane and/or polyisocyanurate, as is understoodin the art. Thus a rigid polyurethane foam can be a rigid polyurethaneand/or polyisocyanurate foam. The term “hydrohalocarbon” is used hereinto mean a compound consisting of carbon, hydrogen, and one or both offluorine and chlorine, and no other elements.

In accordance with the invention, enhancers are provided that are usefulin the reaction of a polyisocyanate and a polyol in the presence of ablowing agent comprising a hydrohalocarbon. Typically, the reaction isperformed in the presence of a urethane catalyst, and typically in thepresence of a surfactant. The enhancer comprises a low molecular weightalcohol or ether, for example di(ethylene glycol) methyl ether.

The process according to the invention can easily be carried out byconventional means for making rigid polyurethane foam, excepting thatthe general preparation of rigid polyurethane foam using ahydrohalocarbon blowing agent, preferably a C1-C4 hydrofluorocarbon, iscarried out using the blowing agent enhancer according to the inventionto improve the blowing agent efficiency.

Polyisocyanate

Rigid polyurethane products made in accordance with the invention may beprepared using any suitable organic polyisocyanates well known in theart for making rigid polyurethane foam including, for example,hexamethylene diisocyanates, isophorone diisocyanates, phenylenediisocyanates, toluene diisocyanates (TDI) and 4,4′-diphenylmethanediisocyanates (MDI). Especially suitable are mixtures of diisocyanatesknown commercially as “crude MDI”, marketed as PAPI by Dow Chemical,which contain about 60% of 4,4′-diphenylmethane diisocyanates along withother isomeric and analogous higher polyisocyanates. Other suitableisocyanates are the 2,4- and 2,6-TDI's individually or together as theircommercially available mixtures. Also suitable are “prepolymers” ofthese polyisocyanates comprising a partially pre-reacted mixture of apolyisocyanate and a polyether or polyester polyol. Typically, the abovepolyisocyanates are used in an amount relative to the polyol toestablish an isocyanate index in the range of 80 to 400.

Polyol

Suitable polyols are those typically used in the art for making rigidpolyurethane foam, including for example polyalkylene ether andpolyester polyols. Polyalkylene ether polyols include poly(ethyleneoxide) and poly(propylene oxide) polymers and copolymers with terminalhydroxyl groups derived from polyhydric compounds, for example diolsand/or triols. Such diols and triols include, as non-limiting examples,ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol,pentaerythritol, glycerol, diglycerol, trimethylol propane, sugars suchas sucrose, and other low molecular weight polyols. Also useful areamine polyether polyols which can be prepared by reacting an amine, suchethylenediamine, diethylenetriamine, tolylenediamine,diphenylmethanediamine, triethanolamine or the like, with ethylene oxideor propylene oxide.

In the practice of this invention, a single high molecular weightpolyether polyol such as described above may be used. Also, mixtures ofsuch high molecular weight polyether polyols, for example mixtures ofdifferent multifunctional materials and/or of compounds having differentmolecular weights or different chemical compositions, may be used.Useful polyester polyols include those produced by reacting adicarboxylic acid with an excess of a diol, for example, adipic acid orphthalic acid anhydride with ethylene glycol or butanediol, or reactinga lactone such as caprolactone with an excess of a diol such aspropylene glycol.

Blowing Agent

The hydrohalocarbon blowing agents used in the present invention formaking rigid foams include, as nonlimiting examples, HCFC(hydrochlorofluorocarbon) compounds, HFC (hydrofluorocarbon) compounds,and mixtures of these. Hydrochlorofluorocarbon compounds comprise atleast one atom of each of hydrogen, chlorine, and fluorine per molecule.Hydrofluorocarbon compounds comprise at least one atom of each ofhydrogen and fluorine per molecule, and no chlorine atoms.

Nonlimiting examples of suitable HCFC's include HCFC-123, HCFC-141b,HCFC-22, HCFC-142b, and mixtures of any of these. Nonlimiting examplesof suitable HFC compounds include HFC-134a, HFC-245fa, HFC-245ca,HFC-236ea, HFC-365mfc, and mixtures of any of these. Preferred blowingagents include HCFC-141b, HFC-134a, HFC-245fa, and mixtures of two ormore of these. More preferred are third generation C1-C4 HFC blowingagents with a molecular weight of 50 to 170 g/mole, a boiling point of−60 to 50 C and preferably an Ozone Depletion Potential (ODP) of <0.10,ODP as described by: Synthesis of the Reports of the Ozone ScientificAssessment Panel, Environmental Effect Assessment Panel Technology andEconomic Assessment Panel, prepared by the Assessment Chairs for theParties to the Montreal Protocol, November, 1991. HFC's meeting thesecriteria include HFC-134a, HFC-236ea, HFC-365mfc and most preferablyHFC-245fa. Mixtures of these may also be used. Water may be included inthe formulation at 0 to 4 pphp (parts per hundred parts of polyol).Other blowing agents which may optionally be used in combination withHFC blowing agents according to the invention include HCFC's, CFC's(chlorofluorocarbons), hydrocarbons such as pentanes, and the like. Inone embodiment of the invention, the blowing agent consists essentiallyof one or more hydrohalocarbons comprising at least one fluorine atomper molecule, either alone or in combination with one or more CFC.

Blowing Agent Enhancer

Blowing agent enhancers according to the invention include compoundshaving a molecular weight less than about 500 g/mol and a molecularformula according to Structure I:

RO—(CH₂CHR″O)_(n)—R′  I

wherein R is selected from the group consisting of a C1-C10 aliphaticgroup, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic group, aC1-C10 aliphatic group comprising a nitrogen atom or oxygen atom, aC5-C10 cycloaliphatic group comprising a nitrogen atom or oxygen atom,and a C7-C10 araliphatic group comprising a nitrogen atom or oxygenatom; R′ is R, hydrogen, acetyl, propionyl, or butyryl, provided thatthe at least one compound has no more than one hydroxyl group permolecule; R″ is hydrogen or C1-C5 alkyl group; and n is an integergreater than or equal to 1. Typically, n is between 1 and 7, inclusive.Mixtures of compounds according to Structure I may also be used.

Suitable C1-C5 alkyl groups useful for R″ include methyl, ethyl,n-propyl, isopropyl, n-butyl, 2-butyl, isobutyl, n-pentyl,2-methylbutyl, and 3-methylbutyl. Suitable C1-C10 aliphatic groupscomprising a nitrogen atom or oxygen atom, and C5-C10 cycloaliphaticgroups comprising a nitrogen atom or oxygen atom, include groups whereina nitrogen atom is incorporated in the form of an amine group and groupswhere an oxygen atom is incorporated as an ether group, a hydroxylgroup, or a carbonyl group. Suitable C7-C10 araliphatic groupscomprising a nitrogen atom or oxygen atom include groups wherein anitrogen atom is incorporated in the form of an amine group or as amember of a heterocyclic ring, and groups where an oxygen atom isincorporated as an ether group, a hydroxyl group, a carbonyl group, oras a member of a heterocyclic ring.

Exemplary compounds according to Structure I include those with twoterminal ether groups, compounds with one terminal ether group and oneterminal hydroxyl group, and acetyl, propionyl, or butyryl esters of thelatter compounds. Preferred enhancers comprise oxyethylene —(CH₂CH₂O)—and/or oxypropylene —(CH₂CH(CH₃)O)— groups.

Blowing agent enhancers according to Structure I containing two terminalether groups include, in one exemplary embodiment, dipropylene glycoldimethyl ether.

Blowing agent enhancers according to Structure I containing one terminalether group and one terminal hydroxyl group include, for example,ethylene glycol monomethyl ether, ethylene glycol monobutyl ether,ethylene glycol phenyl ether, dipropylene glycol monomethyl ether,dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether,tripropylene glycol monopropyl ether, and tripropylene glycol monobutylether.

Particularly useful are propylene glycol monomethyl ether, propyleneglycol monopropyl ether and propylene glycol monobutyl ether. Onepreferred blowing agent enhancer is diethylene glycol monomethyl ether.

Blowing agent enhancers according to Structure I containing one terminalether group and a terminal ester group include acetyl, propionyl, orbutyryl esters of compounds containing one terminal ether group and aterminal hydroxyl group, for example propylene glycol monomethyl etheracetate.

Suitable blowing agent enhancers according to the invention also includecompounds having a molecular weight less than about 500 g/mol and amolecular formula ROH, wherein R is as defined above. Suitable exemplarycompounds in this category include methanol, ethanol, and any isomer ofpropanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, anddecanol.

Mixtures of any of any of these with any of the enhancers represented byStructure I may also be used. Any amount of enhancer may be used,depending upon the desired properties of the resultant foam. Typically,however, the blowing agent enhancer, or mixture of blowing agentenhancers, constitutes at least 2 pphp of the composition, typically atleast 4 pphp, and even more typically at least 5 pphp. Typically, itconstitutes at most 12 pphp, more typically at most 7 pphp, and evenmore typically at most 6 pphp.

Catalyst

A catalyst may be used to promote the reactions forming polyurethanefoams according to the invention. The catalyst composition may be anycatalyst well known in the urethane art such as tertiary amines,organotin compounds, and carboxylate urethane catalysts (gelling and/orblowing). Typical examples of useful catalysts are amine catalysts suchas triethylenediamine, dimethylcyclohexylamine,tetramethylhexanediamine, bis(dimethylaminoethyl)ether,tri(dimethylaminopropyl)hexahydrotriazine, 1-isobutyl-2-methylimidazole,1,2-dimethylimidazole, dimethylaminoethanol, diethylaminoethanol,pentamethyldiethylenetriamine, pentamethyldipropylenetriamine,methylmorpholine, ethylmorpholine, quaternary ammonium salts, salts ofan organic acid and tin catalysts such as dibutyltin dilaurate and thelike.

A catalytically effective amount of the catalyst composition is used inthe polyurethane formulation. More specifically, suitable amounts of thecatalyst composition typically ranges from about 0.01 to 10 parts byweight per 100 parts polyol (0.01 to 10 pphp) in the polyurethaneformulation, preferably 0.5 to 4 pphp.

Surfactant

A surfactant may be used in polyurethane foam compositions and processesaccording to the invention. A number of surfactants suitable for use incontrolling foam properties in polyurethane production are known in theart. Exemplary surfactants include silicone-based surfactants such asare disclosed in U.S. Pat. No. 5,883,142 to Chojnacki et al.

Other Ingredients

Other typical agents that may be used in the polyurethane rigid foamformulations include flame retardants and chain extenders such asethylene glycol and butanediol.

EXAMPLES

A typical range of prior art rigid foam formulations (Table 1) having a1.5-2.5 lb/ft³ (24-40 kg/m³) density (e.g., appliance foam) containing ablowing agent enhancer according to the invention and a third generationblowing agent, for example HFC-245fa, may comprise the followingcomponents in parts by weight (pbw):

TABLE 1 General Rigid Foam Formulation Component pbw Polyol 100 SiliconeSurfactant  1-3 Blowing Agent 20-40 Water  0-3 Catalyst  1-3Polyisocyanate NCO Index = 80-400

As used in Table 1 and hereinafter, the term “NCO Index” meansisocyanate index, as that term is commonly used in the polyurethane art.Use of this term in a table of formulations indicates that theappropriate amount of polyisocyanate should be used in order to achievea formulation having the indicated NCO index.

In the following examples, a specific rigid polyurethane foamformulation (shown in Table 2) was used as a Control formulation forfoam production. Blowing agent enhancers were incorporated intoformulations as shown in Table 3, and the experimental results from foamproduction with the formulations of Tables 2 and 3 are compared in Table4.

TABLE 2 Control Formulation Component pbw Polyol* 100.0 SiliconeSurfactant 4.0 HFC-245fa 35.0 Water 1.3 Amine Catalyst** 2.3Polyisocyanate*** NCO Index = 105 *Sucrose-initiated ethyleneoxide/propylene oxide copolymer with a hydroxyl number of about 350 to400. **A 2:1 wt/wt mixture of Polycat ®5 and Polycat ®41, available fromAir Products and Chemicals, Inc. of Allentown, PA. ***Polymeric MDI,sold under the name Rubinate ®M by Huntsman Polyurethanes of WestDeptford, New Jersey.

TABLE 3 Example Formulation Component pbw Polyol 100.0 SiliconeSurfactant 4.0 HFC-245fa 35.0 Water 1.3 Amine Catalyst 2.3 Blowing AgentEnhancer 6.0 Polyisocyanate NCO Index = 105

Example 1

The ingredients in Tables 2 and 3, except for the polymeric MDI, werecombined and incubated at 10° C. until the mixtures had equilibrated totemperature. The resin was weighed into a paper cup, the polymeric MDIwas added to the cup in an amount such that the isocyanate (NCO) indexwas 105. The mixture was stirred with a high speed mixer for eightseconds, and the cup with the foaming mass was then placed into anL-mold designed for measuring foam flow and other physical properties.The L-mold was heated to 49° C. and was used for initial screening ofblowing agent enhancers. The control formula (Table 2) was used toprepare a reference foam to measure foam flow and foam density forcomparison with foams containing a blowing agent enhancer (Table 3).

Foam flow was determined by measuring the % fill of the L mold when aconstant amount of foam formulation (475 grams) was introduced into themold, with a higher % fill indicating better flow for samples of equalmass. In addition to comparing foam flow and density, foam from each ofthe formulas was evaluated to determine k-factor and compressionstrength. The top 12 inches of the foams were cut into three sectionsthen stored at −30° C. for 72 hours to measure volume change, to verifythat there was less than two percent change, indicating sufficientdimensional stability according to commonly accepted industry standards.The next section of the foam was used to cut a core sample to measurethe k-factor or heat flow in a Lasercomp Fox 200 heat flow meter.

Table 4 is a summary of foam performance data for a number of blowingagent enhancers according to the invention. For each enhancer, thecorresponding % fill in the L-mold and k-factor were recorded.

TABLE 4 Performance of Blowing Agent Enhancers % K-Factor ID CompoundFill (W/mK) 1 Control 92.5 0.0206 (No enhancer) 2 Diethylene glycolmonomethyl ether 99.2 0.0206 3 Tripropylene glycol monobutyl ether 95.60.0206 4 Propylene glycol monobutyl ether 97.7 0.0209 5 Dipropyleneglycol monopropyl ether 94.8 0.0212 6 Propylene glycol monomethyl ether98.0 0.0208 acetate 7 Propylene glycol monomethyl ether 99.0 0.0212 8Ethylene glycol monobutyl ether 96.1 0.0221 9 Dipropylene glycoldimethyl ether 97.2 0.0222 10 Dipropylene glycol monobutyl ether 96.10.0215 11 Dipropylene glycol monomethyl ether 96.7 0.0212 12 Propyleneglycol monopropyl ether 97.7 0.0212 13 Ethylene glycol phenyl ether 95.90.0215 14 Tripropylene glycol monopropyl ether 95.7 0.0216

Compared with the control (1), blowing agent enhancers 2-14 all showedimproved flow (higher value for % fill), with comparable to onlyslightly worse (higher numerical value) k factors. The blowing agentenhancer that yielded the best flow and k-factor was (2), or di(ethyleneglycol) methyl ether.

Example 2

To further demonstrate the efficacy of di(ethylene glycol) methyl etherfor blowing agent reduction, larger scale high-pressure machineevaluations were conducted. The ingredients in Table 3, except for thepolymeric MDI, were combined in a five-gallon pressurized day tank andincubated at 26.7° C. until the mixture had equilibrated to temperature.The polymeric MDI was incubated in a separate five gallon pressurizedday tank and also incubated to 26.7° C. After the ingredients in bothday tanks had been equilibrated, they were mixed together through ahigh-pressure impingement mix head at 13,790 KPa (2000 psi). Thisreacting mass was poured into a 200×20×5 cm mold heated to 49° C.

Enough of the foaming mixture was added to the mold to yield panels atmultiple densities, including minimum fill. Several over-packeddensities were produced to determine the lowest density which passedphysical property requirements. The foam panels were removed from themold after six minutes and aged at 23° C. for 18-24 hours. A20.3×20.3×2.54 cm (8×8×1 inch) portion was cut from the bottom of thepanels and the k-factor was evaluated for each in a Lasercomp Fox 200heat flow meter. Four samples were cut from the top of the panels20.3×10.2×5.1 cm (8×4×2 inch) for determining the density at whichdimensional stability was achieved.

Table 5 collects foam performance data using di(ethylene glycol) methylether at 6 pbw in the formula from Table 3. The objective of thisexample was to match the density and foam performance of the controlwhile maximizing HFC-245fa reduction. The table clearly shows that thedi(ethylene glycol) methyl ether blowing agent enhancer allows for lowerHFC-245fa concentrations, with no significant penalties to foam thermalproperties and an improvement to the compression strengths. Compressionstrength values are a measure of the force needed to physically crushthe foam until failure. Higher force relates to improved foam mechanicalproperties, giving the final product (e.g. a refrigerator) structuralintegrity. Table 5 illustrates that a 19% reduction of HFC-245fa isattainable by use of di(ethylene glycol) methyl ether as a blowing agentenhancer to achieve foams of equivalent k-factor, while maintainingequal or even improved compression strength.

TABLE 5 Reduction of Blowing Agent Use Level Minimum Fill K- CompressionEnhancer HFC-245fa (Density Factor Strength (KPa) Formula (pphp) (pphp)Kg/m³) (W/mK) Perp./Parallel 1 None 35.2 32.84 0.0195 138/159 2 6.0 28.532.68 0.0195 165/193 3 6.0 28.5 32.04 0.0198 159/200 4 6.0 28.5 33.000.0196 152/186

The foregoing experimental data indicate that, in the production ofrigid polyurethane foams using a hydrohalocarbon blowing agent,particularly HFC-245fa, use of blowing agent enhancers according to theinvention allows the production of foams with a reduced amount ofblowing agent, while retaining at least equal physical properties to areference foam with a higher level of blowing agent and none of theenhancer. In some cases, compression strength is improved with use ofthe enhancer.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, it is intended that the scope ofthe claims that follow includes various modifications that may be madein the details while nevertheless achieving the effects of thisinvention.

1. A composition for producing a polyurethane foam, the compositioncomprising a polyol a blowing agent comprising a hydrohalocarbon, and ablowing agent enhancer comprising at least one compound having amolecular weight less than about 500 g/mol and a molecular formula ofRO—(CH₂CHR″O)_(n)—R′; wherein: R is selected from the group consistingof a C1-C10 aliphatic group, a C5-C10 cycloaliphatic group, a C7-C10araliphatic group, a C1-C10 aliphatic group comprising a nitrogen atomor oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogen atomor oxygen atom, and a C7-C10 araliphatic group comprising a nitrogenatom or oxygen atom; R′ is selected from the group consisting of R,hydrogen, acetyl, propionyl, and butyryl, provided that the at least onecompound has no more than one hydroxyl group per molecule; R″ ishydrogen or a C1-C5 alkyl group; and n is an integer greater than orequal to
 1. 2. The composition of claim 1, wherein the at least onecompound comprises no hydroxyl groups.
 3. The composition of claim 1,wherein R″ is hydrogen or methyl.
 4. The composition of claim 1, whereinthe at least one compound comprises dipropylene glycol dimethyl ether.5. The composition of claim 1, wherein the at least one compoundcomprises propylene glycol monomethyl ether, propylene glycol monopropylether, propylene glycol monobutyl ether, or a mixture of any of these.6. The composition of claim 1, wherein the at least one compoundcomprises diethylene glycol monomethyl ether.
 7. The composition ofclaim 1, wherein the hydrohalocarbon comprises at least one fluorineatom per molecule.
 8. The composition of claim 1, wherein the blowingagent comprises HCFC-123, HCFC-141b, HCFC-22, HCFC-142b, HFC-134a,HFC-245fa, HFC-245ca, HFC-236ea, HFC-365mfc, or a mixture of any ofthese.
 9. The composition of claim 1, wherein the blowing agentcomprises HCFC-141b, HFC-134a, HFC-245fa, or a mixture of any of these.10. The composition of claim 1, wherein the blowing agent comprises aC1-C4 hydrofluorocarbon having a molecular weight between 50 and 170g/mol, a boiling point between −60° C. and 50° C., and an OzoneDepletion Potential less than 0.10.
 11. The composition of claim 1,wherein the blowing agent comprises HFC-134a, HFC-236ea, HFC-365mfc,HFC-245fa, or a mixture of any of these.
 12. The composition of claim 1,wherein the blowing agent comprises HFC-245fa.
 13. The composition ofclaim 1, additionally comprising a catalyst.
 14. The composition ofclaim 1, additionally comprising a surfactant.
 15. A composition forproducing a polyurethane foam, the composition comprising a polyol, apolyisocyanate, HFC-245fa, and one or both of diethylene glycolmonomethyl ether and dipropylene glycol dimethyl ether.
 16. A method ofmaking a polyurethane foam, the method comprising combining a polyol anda polyisocyanate in the presence of 1) a blowing agent comprising ahydrohalocarbon and 2) a blowing agent enhancer comprising at least onecompound having a molecular weight less than about 500 g/mol and amolecular formula of RO—(CH₂CHR″O)_(n)—R′; wherein: R is selected fromthe group consisting of a C1-C10 aliphatic group, a C5-C10cycloaliphatic group, a C7-C10 araliphatic group, a C1-C10 aliphaticgroup comprising a nitrogen atom or oxygen atom, a C5-C10 cycloaliphaticgroup comprising a nitrogen atom or oxygen atom, and a C7-C10araliphatic group comprising a nitrogen atom or oxygen atom; R′ isselected from the group consisting of R, hydrogen, acetyl, propionyl,and butyryl, provided that the at least one compound has no more thanone hydroxyl group per molecule; R″ is hydrogen or a C1-C5 alkyl group;and n is an integer greater than or equal to
 1. 17. The method of claim16, wherein the hydrohalocarbon comprises at least one fluorine atom permolecule.
 18. A composition for producing a polyurethane foam, thecomposition comprising a polyol, a polyisocyanate, a blowing agentcomprising a hydrohalocarbon, and a blowing agent enhancer comprising atleast one compound having a molecular weight less than about 500 g/moland a molecular formula ROH, wherein: R is selected from the groupconsisting of a C1-C10 aliphatic group, a C5-C10 cycloaliphatic group, aC7-C10 araliphatic group, a C1-C10 aliphatic group comprising a nitrogenatom or oxygen atom, a C5-C10 cycloaliphatic group comprising a nitrogenatom or oxygen atom, and a C7-C10 araliphatic group comprising anitrogen atom or oxygen atom, provided that the at least one compoundcomprises only one hydroxyl group per molecule.
 19. The composition ofclaim 18, wherein the hydrohalocarbon comprises at least one fluorineatom per molecule.
 20. The composition of claim 18, wherein the at leastone compound is selected from the group consisting of methanol, ethanol,isomers of propanol, isomers of butanol, isomers of pentanol, isomers ofhexanol, isomers of heptanol, isomers of octanol, isomers of nonanol,isomers of decanol, and mixtures of any of these.
 21. A polyurethanecomposition comprising a product of a reaction between a polyol and apolyisocyanate, the reaction taking place in the presence of 1) ablowing agent comprising a hydrohalocarbon and 2) a blowing agentenhancer comprising at least one compound having a molecular weight lessthan about 500 g/mol and a molecular formula of RO—(CH₂CHR″O)_(n)—R′;wherein: R is selected from the group consisting of a C1-C10 aliphaticgroup, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic group, aC1-C10 aliphatic group comprising a nitrogen atom or oxygen atom, aC5-C10 cycloaliphatic group comprising a nitrogen atom or oxygen atom,and a C7-C10 araliphatic group comprising a nitrogen atom or oxygenatom; R′ is selected from the group consisting of R, hydrogen, acetyl,propionyl, and butyryl, provided that the at least one compound has nomore than one hydroxyl group per molecule; R″ is hydrogen or a C1-C5alkyl group; and n is an integer greater than or equal to
 1. 22. Acomposition for producing a polyurethane foam, the compositioncomprising 1) one but not both of a polyol and a polyisocyanate, 2) ablowing agent comprising a hydrohalocarbon and 3) a blowing agentenhancer comprising at least one compound having a molecular weight lessthan about 500 g/mol and a molecular formula of RO—(CH₂CHR″O)_(n)—R′;wherein: R is selected from the group consisting of a C1-C10 aliphaticgroup, a C5-C10 cycloaliphatic group, a C7-C10 araliphatic group, aC1-C10 aliphatic group comprising a nitrogen atom or oxygen atom, aC5-C10 cycloaliphatic group comprising a nitrogen atom or oxygen atom,and a C7-C10 araliphatic group comprising a nitrogen atom or oxygenatom; R′ is selected from the group consisting of R, hydrogen, acetyl,propionyl, and butyryl, provided that the at least one compound has nomore than one hydroxyl group per molecule; R″ is hydrogen or a C1-C5alkyl group; and n is an integer greater than or equal to
 1. 23. Thecomposition of claim 22, wherein the hydrohalocarbon comprises at leastone fluorine atom per molecule.
 24. A composition for producing apolyurethane foam, the composition comprising a polyol, apolyisocyanate, a blowing agent comprising a hydrohalocarbon, and ablowing agent enhancer comprising at least one compound having amolecular weight less than about 500 g/mol and a molecular formula ofone of ROH and RO—(CH₂CHR″O)_(n)—R′; wherein: R is selected from thegroup consisting of a C1-C10 aliphatic group, a C5-C10 cycloaliphaticgroup, a C7-C10 araliphatic group, a C1-C10 aliphatic group comprising anitrogen atom or oxygen atom, a C5-C10 cycloaliphatic group comprising anitrogen atom or oxygen atom, and a C7-C10 araliphatic group comprisinga nitrogen atom or oxygen atom; R′ is selected from the group consistingof R, hydrogen, acetyl, propionyl, and butyryl, provided that the atleast one compound has no more than one hydroxyl group per molecule; R″is hydrogen or a C1-C5 alkyl group; and n is an integer greater than orequal to
 1. 25. The composition of claim 10 wherein the enhancercomprises at least one ether.
 26. The composition of claim 25 whereinthe composition further comprises at least one silicone-basedsurfactant.
 27. The composition of claim 26 wherein the blowing agentfurther comprises water.